Analog to digital converters (ADCs) are used in a variety of applications in order to convert a detected analog signal into a digital signal. As technology nodes decrease, supply voltages also decrease. However, time resolution has increased in response to decreasing technology nodes. As a result, time to digital converters (TDCs) are used to perform time-domain processing to convert detected signals into digital signals.
In some approaches, a counter is used to determine a number of clock cycles between a start signal of a reference voltage and a clock stop signal which occurs after the reference voltage is equal to a voltage of the detected analog signal. A frequency of the clock used for the counter is determined based on a number of detecting elements connected to the counter. In some approaches, the counter is separated into a coarse counter and a fine counter. The coarse counter is used to determine a number of clock cycles, while the fine counter is used to interpolate between clock cycles using various delays of the clock.
In some approaches, the coarse counter and the fine counter are used sequentially in order to convert the detected signal into a digital signal. The coarse counter is used to count a number of cycles between the start signal and the clock stop signal; and the fine counter is used to count a number of cycles between a stop signal and the clock stop signal. The stop signal occurs when the reference voltage is equal to the voltage of the detected signal. A difference between the number of cycles counted by the coarse counter and a number of cycles counted by the fine counter is used to determine the time domain which is converted into the digital signal.